(1) Field of the Invention
The present invention relates to a tank provided with an over-pressure valve, and also to an aircraft and to a method implementing the tank.
(2) Description of Related Art
An aircraft may include a pressurized filler circuit for filling at least one fuel tank on the ground and/or in flight. The pressurized filler system may possibly allow fuel to be extracted from the tank by suction.
Certification regulations require means for limiting the quantity of fuel in a tank in order to avoid damage in the event of said quantity exceeding a threshold. For example, the regulation known under the reference CS 29.979 makes provision for such an installation.
A filler system may thus be fitted with solenoid valves in order to stop filling as from there being a certain quantity of fuel present in at least one tank.
Furthermore, a fuel storage system of an aircraft includes at least one vent circuit for connecting the tank to the outside air. Such a vent circuit may possess two types of valve in order to allow air to pass from a tank to an outside medium, and vice versa, namely:                a first type of valve known as an “air-no-fuel valve” that closes when in contact with fuel; and        a second type of valve known as a “roll-over valve” that closes as from a threshold angle of inclination independently of the presence or absence of contact with fuel.        
A roll-over valve may include a ball suitable for moving as a function of the angle of inclination of the aircraft in order to shut off the vent circuit as from a threshold angle, e.g. as a result of the aircraft rolling over. A roll-over valve thus allows at least one tank to be vented so long as the aircraft is operating under normal flight conditions.
A vent circuit may then possibly allow fuel to be discharged in the event of a solenoid valve malfunctioning. Nevertheless, certain dimensioning constraints can lead to a venting circuit being installed that does not have dimensional characteristics that allow this degraded mode of operation to take place. The diameter of the pipe in a vent circuit may be too small relative to the filling rate to allow excess fuel to be discharged in real time.
Under such circumstances, an aircraft may include at least one over-pressure valve in order to avoid the tank being put under pressure in the event of a malfunction preventing a solenoid valve from being closed. Under such accidental circumstances, the over-pressure valve opens as from a pressure threshold in order to discharge excess fuel from a tank.
In terms of configuration, two types of over-pressure valve installation are commonly used on a machine.
In a first configuration, the aircraft has a discharge pipe connected to a top portion of a tank, the pipe being placed outside the tank. An over-pressure valve is then secured to the discharge pipe. The over-pressure valve is then arranged outside the fuel tank.
Consequently, the over-pressure valve is not continuously in contact with fuel. That first configuration thus presents the advantage of avoiding fuel seepage as a result of an over-pressure valve being practically continuously in contact with fuel.
However, the aircraft must then provide sufficient space to allow the discharge pipe and the over-pressure valve to be installed.
Furthermore, it can be difficult to arrange an over-pressure valve in that first configuration, since the fuel discharge line needs to be arranged so as to avoid coming close to sensitive zones of the aircraft (zones that might be subjected to high temperatures, zones where maintenance personnel might take action, . . . ).
In a second configuration, the aircraft has a discharge pipe extending inside the tank in order to open out in the outside air, e.g. under the fuselage. An over-pressure valve is then secured to the discharge pipe. The over-pressure valve is then arranged inside the fuel tank.
That second configuration would appear not to suffer from the drawbacks of the first configuration because of the arrangement of the discharge line inside the tank.
Nevertheless, the over-pressure valve is then in contact with the fuel and runs the risk of seeping.
A manufacturer must thus select one or the other of those configurations depending on the constraints with which the manufacturer is confronted.
Document WO 2010/131099 discloses a breather valve for a fuel system on board an aircraft, serving in particular to facilitate pressurizing the tank.
Document WO 2012/123941 describes a device including simultaneously a roll-over valve, an over-pressure valve, and a pressure retention valve.
Document US 2008/0078457 discloses an over-pressure valve for an aircraft fuel tank. That over-pressure valve has two levels of response to a pressure difference between the inside and the outside of a tank. The second level is in addition to the first level in the event of a failure, e.g. because of ice.
Documents US 2009/236350, U.S. Pat. No. 4,376,446, and U.S. Pat. No. 5,277,217 are remote from the invention.
For example, Document US 2009/236350 describes a tank ventilation system and not a flow line for discharging excess fuel.
That ventilation system has a canister in communication via a set of pipes with two valves housed inside a tank. One valve includes movable float means, and the other valves includes movable float means upstream from two valves that open under a predetermined pressure of a gas.